Ball peening or forming is a process by which large wrought forms and shapes of metal may be surface treated or shaped by impacting a media of significant mass over the surface of the work piece. Generally the media consists of metal balls which are applied in large quantities across the width of the work piece as the work piece moves through the delivery system. The processes of the prior art utilize a variety of means for applying the media to the work piece depending on the job to be performed.
A high velocity impact may be provided by a pneumatically or hydraulically powered mechanism which forces the media under pressure through a nozzle. A system of this type is shown in U.S. Pat. No. 3,423,976. There are several limitations which are inherent in this type of construction. The media feed system is unduly restrictive and elaborate and air delivery and nozzle size restrictions severely limit the size and amount of peening media delivered. This type of ball forming system is a high air pressure system and will not deliver large size media uniformly at low air pressures or in great quantity.
Another type of delivery apparatus is shown in U.S. Pat. Nos. 3,491,563 and 3,660,943 which employ a rotating wheel or impeller to centrifuge the media against the work piece. This type of apparatus is also limited to the application of relatively small media at a high speed and the media feed system becomes more complicated with a resulting tendency to clog with large media. In addition, only a narrow width of media delivery is possible and the amount of media delivered is reduced with increasing media size.
It is generally desirable, in order to obtain the smoothest finish, to apply media of a high mass to the work piece at a slow speed. One way of accomplishing this is to construct the apparatus utilizing a gravity delivery system as shown in U.S. Pat. No. 3,705,511. This system provides the ability to use a very large size ball and its feed system is very simple. It is limited however by the height of the building as to the impact that can be achieved. It is the purpose of this invention to modify the gravity type system to eliminate the inherent restrictions while maintaining the simplicity of design.